The present disclosure relates to temperature control systems for controlling the temperature of a heated device.
Temperature control systems may comprise a thermostat to control flow of coolant between a heated device and a heat exchanger. The heated device may be, for example, an engine that heats up as it operates. The heat exchanger may be, for example, a radiator associated with the engine to cool liquid coolant that circulates through the engine for cooling the engine. The thermostat may be used to direct coolant from the engine back to the engine so as to bypass the radiator to warm up the engine when the engine is cold. When the engine reaches a desired operating temperature, the thermostat may allow coolant to begin to flow to the radiator to prevent engine overheating.
The present invention comprises one or more of the following features or combinations thereof. A thermostat apparatus is provided to control the flow of coolant between a heated device and a heat exchanger to control the temperature of the heated device. The thermostat apparatus comprises a thermostat and a positioner for establishing different operating temperatures for the thermostat.
The thermostat may comprise a valve, a first piston, and a first thermal expansion device cooperatively associated to move the valve in response to temperature. In such a case, the first thermal expansion device comprises a temperature responsive first expansion agent (e.g., wax) to relatively move the first piston and the first thermal expansion device to move the valve away from a valve seat to allow flow of coolant from the heated device to the heat exchanger.
The positioner may comprise a second piston, a second thermal expansion device comprising a temperature responsive second expansion agent (e.g., wax), and a heater. The heater heats the second expansion agent to relatively move the second piston and second thermal expansion device which, in turn, relatively moves the first piston and first thermal expansion device between a higher valve actuation temperature position establishing a higher valve actuation temperature for actuating the valve and a lower valve actuation temperature position establishing a lower valve actuation temperature for actuating the valve.
The heater may be an electric heater (e.g, an electric positive thermal coefficient ceramic heater). A controller (e.g., an engine control module) may be electrically coupled to the electric heater via a relay switch either to supply electric power to the heater to xe2x80x9cactivatexe2x80x9d the positioner or not to supply electric power to the heater to xe2x80x9cde-activatexe2x80x9d the positioner. When the positioner is activated, the heater heats the second expansion agent to extend the second piston from the second thermal expansion device. Upon extension, the second piston causes the first piston to retract into the first thermal expansion device a predetermined distance from the higher valve actuation temperature position to the lower valve actuation temperature position to establish the lower valve actuation temperature for actuating the valve. When the positioner is de-activated, the first piston and first thermal expansion device will actuate the valve at the higher valve actuation temperature.
A heat sink may be positioned in the second expansion agent to distribute heat from the heater into the second expansion agent. There may be two such heat sinks, one on each side of the heater. Each heat sink may have a plurality of tines extending in the second expansion agent.
The positioner may comprise a stroke limiter between the positioner piston and thermostat piston to limit the stroke of the thermostat piston to the predetermined distance. The stroke limiter comprises a spring and a spring housing around the spring. When the positioner piston strokes the predetermined distance, the spring housing engages a stroke-limiting surface to stop movement of the thermostat piston. Any excessive stroke of the positioner piston is then taken up by the spring so that the thermostat piston moves only the predetermined distance to achieve a corresponding change in valve actuation temperature.
The thermostat may be positioned in a coolant passageway so that the first expansion agent will react to the temperature of coolant in the coolant passageway. The positioner may be positioned outside the coolant passageway so that the second expansion agent will react to heat from the heater rather than the temperature of coolant in the coolant passageway to promote control of the positioner.
Additional features and advantages of the apparatus will become apparent to those skilled in the art upon consideration of the following detailed description exemplifying the best mode of the disclosure as presently perceived.